1. Field of the Invention
The present invention relates to a signal processing device, image sensing system, and signal processing method.
2. Description of the Related Art
There has conventionally been proposed an amplifier type image sensing system, particularly a CMOS (Complementary Metal Oxide Semiconductor) image sensing system, as disclosed in Japanese Patent Laid-Open No. 2001-24949. Compared to a CCD image sensing system, the CMOS image sensing system has various merits: 1) it has low noise, 2) it has small power consumption, 3) it is drivable by a single power supply, and 4) its light-receiving portion and peripheral circuit are manufacturable by the same process.
In the CMOS image sensing system, when extremely bright light enters a pixel in capturing an image of the sun or the like, the luminance component of the pixel signal of the pixel attenuates, and the gray level of the pixel may drop to black (bright light image inversion phenomenon).
To avoid this phenomenon, according to the technique disclosed in Japanese Patent Laid-Open No. 2001-24949, it is determined that bright light image inversion phenomenon has occurred when the signal level reaches the saturation signal level. A process (to be referred to as a removal process hereinafter) to remove a pixel reset signal from an electrical signal output from the photoelectric converter stops unconditionally. This can prevent bright light image inversion phenomenon.
However, even if the signal level reaches the saturation signal level, bright light image inversion phenomenon may or may not occur. In this case, stopping the removal process unconditionally may increase fixed-pattern noise. As a result, noise may be superposed in the finally obtained image, degrading image quality.